If I'm not mistaken, the one you're missing is the Invisible frog.

Just after exiting the dark mountain that's part of the main route, there's a golden tunnel. There's a light drizzle in the area. There should be an eagle teleporting stone nearby so the teleport melody works. (the right most stone)

The frog is invisible but you can see sparkles around it's silhouette. It's located on the far-left of that screen (in the water), just before jumping off the edge.

You can only get to that part of the mountain if you send a bird up first with a glow bug. Inside the mountain just before the exit there is a verfical parth guarded by masks. The large birds that get you there from the earlier section (there are two) transport you up and get snapped by the masks if you just follow the story, but if you send one up first with a glow bug for the nest and take the next bird yourself up to the nest you can unlock the area on top of the mountain, which as Detective Lunpe says contains the invisible frog. It also has a drop point for the gold tokens that unlock the door in the lava mountain.

awesome.. thanks to you both!